1. Field of the Invention
This invention relates to apparatus for processing MOS-LSI devices and more particularly to removing unwanted particles and contamination from the surfaces of dice or chips without damage thereto.
2. Description of the Prior Art
In the fabrication of MOS-LSI devices, foreign particles and contamination frequently contribute to the low yield of dice or chips which have been scribed and divided from device wafers. Most of the device dice or chips that survive scribing and separation have been coated with a protective film or layer such as silox for preventing physical changes or moisture from accumulating on the metallized conductors. Even the protective layer has an affinity for particulate and contamination. The coated dice or chips are evaluated for particulate at a die visual inspection with a microscope on the order of 100X power. At die visual inspection, there are two major modes that account for the greatest loss of good electrical dice, viz. surface particles and faults on, within, or under the silox passivation layer. Of course, if the die fails due to electrical shorting, it cannot be saved; but failures due to particulate may be saved by further cleaning. Some of the contamination results from the cleaning solvents, plastic fragments from the carrying trays and other handling steps. Particles can be oxidized and/or removed when excited by an RF field in oxygen plasmas, but this method of removal is unacceptable because there is risk of latent electrical damage due to surface charges. Foreign particles may also be removed by laser energy without visible damage to the protective coating (silox) or metallization beneath, but there is also risk of latent electrical damage due to surface charges. Particles are also removed by manual or mechanical means. However, many plastic bristles, pine splinters and bamboo splinters leave fragments on the surface. This method is not recommended because the dice or chips are small, fragile and difficult to handle. Additionally, the original particles are numerous and frequently are close to the wire bonding sites thereby increasing the risk of damage to the exposed metallization.
Since the trend is to increase the size of the dice, as component density requirements increase any particulate on the dice wafer could lead to failure at die visual inspection or affect the performance of the devices. Therefore, it is important to utilize processes and tooling which are not complex and where breakdown and down-time does not result in low efficiency. The methods and apparatus utilized for effective cleaning of dice or chips must be geared to easily cycle the dice repeatedly with inspection checks along the various steps involved thereby increasing the yield and lowering the cost of producing usable device die chips.